1. Evolution
of
Populations
Evolution Unit

2. TEACHER NOTES
 This PowerPoint was revised June
26, 2008.
 Items marked with a red arrow
should be emphasized.
 When using the PPT with the
Population Graphs worksheet,
discuss the PPT information and
then fill out the appropriate
sections of the worksheet.

3. Population
 What is a population?
Number of Individuals of the
Same Species that
Live together in one area or place

4. Factors That Control
Population Growth
 A population’s biotic potential is
the size it would be if nothing
stopped it.
 Why don’t populations grow
indefinitely?

5. Factors That Control
Population Growth
 What determines the population
number of an ecosystem (or
planet)?
(Think in terms the basics that plants,
animals and ourselves need to survive.)

6. Factors That Control
Population Growth
 Populations don’t grow indefinitely
because of Limiting Factors.
 The major limiting
factors are FWSS:
–Food
–Water
–Shelter
–Space

7. Factors That Control
Population Growth
 Carrying Capacity is the maximum
number of individuals the
environment can support.
 Carrying capacity is
closely associated with
the availability of limiting
factors.

8. Factors That Control
Population Growth
 Does carrying capacity for an area
ever change? Why or why not?
?
?
carrying capacity

9. Population Growth Rate
Exponential “J” Curve
 Some populations start slow and
then have a burst of growth.
 This is called
EXPONENTIAL
growth.
 What shape
curve does it
have?
70
60
50
40
30
20
10
0
0 1 2 3 4 5 6
Time

10. 70
60
50
40
30
20
10
0
0 1 2 3 4 5 6
Time
Population Growth Rate
Exponential “J” Curve
 What is the slow
almost flat
growth called?
 What is the fast
almost straight
up growth
called?
Lag
Exponential
A
B

11. What is this curve
called?
What is this phase?
What is this phase?
B.
A.

12. Population Growth Rate
Logistic “S” Curve
 Some populations start slow, have
a burst of growth, then level off.
 This is called
LOGISTIC
growth.
 What shape is
the curve?
600
500
400
300
200
100
0
0 10 20 30
Time (in days)
Population

13. Population Growth Rate
Logistic “S” Curve
 Logistic curves have a lag phase
and an exponential phase.
 Where are
they on this
graph?
600
500
400
300
200
100
0
0 10 20 30
Time (in days)
Population
A
B
C
D

14. Population Growth Rate
Logistic “S” Curve
 The almost flat, slightly up/down
line is called stabilization.
 What letter
represents
stabilization
on the
graph?
600
500
400
300
200
100
0
0 10 20 30
Time (in days)
Population
A
B
C
D

15. Population Growth Rate
Logistic “S” Curve
 What is carrying capacity?
 What letter represents it?
 Why does the
population
stabilize at “A”?
600
500
400
300
200
100
0
0 10 20 30
Time (in days)
Population
A
B
C
D

16. Population Growth Rate
Logistic “S” Curve
 What will happen to a population if
it goes over the carrying capacity?
 What will
happen to a
population if it
drops under
the carrying
capacity?
600
500
400
300
200
100
0
0 10 20 30
Time (in days)
Population
K
K carrying capacity
lag
exponential
stabilization

17. Population Growth Rate
Logistic “S” Curve
What is this?
What is this?
What is this?
What is this?
Why does it
rise and fall
slightly?
A.
C.
B.
D.

18. Natural Selection
and Populations
Recall Darwin’s
Concepts of Natural Selection
 variation exists in all species
 organisms produce more offspring than
can survive
 competition for limited life resources
 survival of the fittest (most suited to
the environment)
 descent with modification

19. Natural Selection
and Populations
 Relate variation and offspring
production to the population at B
and C.
 Describe
competition
when the
population
reaches A.
600
500
400
300
200
100
0
0 10 20 30
Time (in days)
Population
A
B
C
D

20. Natural Selection
and Populations
 Relate survival of the fittest with
the population at D.
 Describe the
population at
D in terms of
descent with
modification
and variation.
600
500
400
300
200
100
0
0 10 20 30
Time (in days)
Population
A
B
C
D

21. Natural Selection
and Populations
 Relate the five concepts of natural
selection to Graph #3.
 Variation
 Numbers increase
 Competition
 Survival of the
fittest
 Descent with
modification
Event C
Event B
Event D
Event A

22. Human Population
 What kind of curve is world
population growth?

23. Human Population
 Where is the lag phase?
 The exponential phase?

24. Human Population
 Where is the carrying capacity?

25. Human Population
 What historical event could have
caused the dip at the arrow?

26. Human Population
Consider the Black Death Plague
as an environmental change.
 Describe the population after the
Black Death (yellow arrow) in terms
of variation and survival of the fittest.

27. Human Population
 Why would the industrial revolution
cause a population increase?
(think in terms of FWSS and carrying capacity)

28. Human Population
 Where do we go from here?
Children
per Woman:
High 2.5
Medium 2.0
Low 1.6

29. Human Population
 What is the Earth’s carrying capacity?
When will
we reach
it?
Who will
survive?
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

30. Works Cited
 “Big Horn Sheep”, “Seabirds”. No date. Online
Image. Free Stock Photos. June 15, 2004.
<http://www.geekphilosopher.com/MainPage/bk
gLinksPhotos.htm>